PEDOGENETIC DIFFERENTIATION OF SOIL PROPE RTIES IN AGGREGATES

Besides the pedogenetic differentiation of soils in horizons a differe ntiation within horizons across aggregates seems possible. The objecti ve of this study is to check if there is a differentiation of soil pro perties across aggregates. From a Braunerde, a Podzol-Braunerde, 2 Pod sols from Bavaria and Slovakia aggregates of 10-30 mm In diameter were selected manually from both topsoil and subsoil horizons and mechanic ally fractionated into a core and a surface fraction. In the aggregate fractions C-org, Al-o, and Fe-d were determined. C-org is generally d epleted in the surface fractions of the A-horizons compared I to the c ore fractions; This may be due to favoured microbial degradation of or ganic matter compared to the aggregate core and preferential leaching of organic C. In the subsoil horizons of the Braunerde C-org is lower in the aggregate surface fraction, in the Podzol, however, it is highe r. In Podzols preferential C-input and sorption to aggregate surfaces seems to dominate. Lower Al-o- and Fe-d-concentrations in the aggregat e surface fractions of all A-horizons may be explained by preferential acidification of aggregate surfaces as the aggregate surfaces mainly buffer the proton input into structured mineral soils. In the B-horizo ns only in Braunerde Al-o and Fe-d are lower in the aggregate surface fractions than in the core fractions. The Podzol B-horizons show prefe rential illuvial enrichment of sesquioxides at aggregate surfaces. Thu s, pedogenesis results in the differentiation of soil properties not o nly between horizons but also within horizons on the level of aggregat es. The resulting different chemical properties of aggregate surface a nd core fractions may affect the sorption capacity of structured soils .